Interference from terrestrial microwave systems is a major consideration in planning the location of earth stations for satellite communication systems. As the desirable locations for both microwave relay stations and satellite earth stations tend to be the same, there will exist some situations in which interference cannot be avoided.
Adaptive interference suppression systems have been designed to deal with this problem. In this regard see, for example, "An Adaptive Co-channel Interference Suppression System to Suppress High Level Interference in Satellite Communication Earth Terminals" by E. D. Horton in National Telecommunication Conference Record, Dallas, Tex., Nov. 29-Dec. 1, 1976, Sect. 13.4, pp. 1-5 and "Suppression of Co-channel Interference with Adaptive Cancellation Devices at Communications Satellite Earth Stations" by P. D. Lubell et al in ICC 77 Conference Record, June 12-15, 1977, Chicago, Ill., Vol. 3, pp. 49.3-284-49.3-289. In these disclosed systems, an independent sample of the interfering signal is obtained, the phase and amplitude of which is adjusted by an adaptive filter to provide an estimate of the interference in the received signal. This estimate is then subtracted from the received signal to give the undistorted desired signal and a residue from the subtract operation. The response of the adaptive filter depends on the correlation between this residue and the interference sample.
The correlation in the cited articles is done either at RF or IF. The IF realization requires an independent down converter for the interference sample adding substantially to the cost of the system. The RF realization presents problems when a number of interfering sources are present. The correlation is done over the whole 500 MHz bandwidth and due to the frequency dependence of the side lobe pattern of the main antenna one can get varying degrees of cancellation and enhancement over the band. Therefore, the problem remaining in the prior art is to provide an adaptive interference suppression arrangement which can avoid the above-mentioned independent down converter and provides interference suppression in a desired band of frequencies.